This project concentrates on two aspects of the structure of bacterial ribosomes. The first is details of the structure at or near functional sites. Of special interest are the tRNA binding sites, regions near the ends of the ribosomal RNAs, and the sites of interaction of the antibiotics erythromycin and streptomycin. Fluorescent derivatives of ribosomal components and ligands are prepared which still maintain significant functional activity. Distances between pairs of dyes are measured by singlet energy transfer. Individual derivatives are used for kinetic and equilibrium studies of ribosome-ligand interaction. Quenching and polarization measurements allow the accessibility and flexibility of sites to be examined. Components of functional sites are identified by affinity labeling. Site-specific reaction is insured by coupling covalent and modification to subsequent function. The second focus is the structure and function of the RNAs within the ribosome. Various chemical techniques for examining the location and properties of regions of ribosomal RNAs are being examined. Tritium exchange is being used to detect exposed purine residues. Psoralen derivatives are used as photo crosslinking agents specific for double stranded RNA. The crosslink locations are mapped by electronmicroscopy.